The primary objective of this study is to define the efficacy of sustained release (SR) moxonidine in Stage 1 and Stage 2 hypertensive patients based on the change from baseline to endpoint in sitting diastolic blood pressure measured at trough compared with that of placebo. It is believed that the new SR formulation will minimize the dose-limiting side effects of somnolence and dry mouth observed in immediately release (IR) treated hypertensive patients. The secondary objectives are to determine the effect of SR moxonidine compared with placebo on: a) sitting diastolic blood pressure responder rate at trough; sitting systolic and diastolic trough/peak ratios b) systolic and diastolic blood pressures c) heart rate d) glycosylated hemoglobiin A1c e) lipid profile f) adverse clinical and laboratory events This is a randomized, placebo-controlled, double-blind, multicenter study in patients with Stage 1 or Stage 2 essential hypertension. The study will consist of three periods: (1) placebo lead-in; (2) parallel active treatment; and (3) washout. The study is single-blind during the placebo lead-in and washout periods and double-blind during the parallel active treatment period. During randomization patients will be assigned one of four treatments: moxonidine, 1.5 mg, 1.0 mg 0.5 mg or placebo. Additionally, plasma drug levels will be collected for pharmacokinetic modeling at the University Hospitals of Cleveland site only.